Mobile telephone systems include a variety of services and functions beyond simple direct voice communication. Once scarce and expensive, mobile communication devices are now so common that most people own at least one. Mobile phones allow users to communicate from virtually anywhere.
Many cellular systems today comprise either a subscriber identity module (a “SIM” card) or a universal SIM (a “U/SIM” card) that is used for authenticating cellular subscription, services, billing, as well as other purposes. These technologies are denoted collectively as U/SIM. The U/SIM card is typically in a form factor that is removable by the user, which can make it possible to carry mobile subscription information and data through different types and generations of mobile communication devices (e.g., cellular phones).
The U/SIM card contains a microchip that houses a microprocessor and a memory. The card stores a mathematical algorithm that encrypts voice and data transmissions, which makes it nearly impossible to “listen in” on calls. The U/SIM also identifies the user to the mobile network as a legitimate caller. The interfaces between the mobile handset and the U/SIM card are fully standardized, and there are already specifications in place for third generation handsets and U/SIMs.
In addition to being employed with a mobile communication device, the U/SIM card can be utilized in connection with an analog telephone adapter (ATA), which can couple a telephone to a cellular network via Voice over IP (VoIP). SIM-enabled ATA devices (hereinafter referred to as SIM-ATA) generally require a SIM that is programmed with the customer subscription information. SIM-ATA devices can be employed in the subscriber's home and/or office and can be useful when cell coverage does not extend into a potential area of use or fails to provide adequate signal strength.